A manufacturing process for a semiconductor device includes a variety of steps such as a lithography step, a dry-etching step, and an ion-planting step. After completion of each step and before moving to the next step, a cleaning step for removing impurities and a residue left on a wafer surface to clean the wafer surface, a rinsing step for removing a chemical residue after the cleaning, and a drying step are implemented.
For example, in a wafer cleaning treatment after the etching step, a chemical solution is supplied to the wafer surface for the cleaning treatment, and pure water is thereafter supplied to perform a rinsing treatment. After the rinsing treatment, there is performed a drying treatment for removing the pure water remaining on the wafer surface and drying the wafer.
As a method for performing the drying treatment, there are for example known rotary drying in which the pure water on the wafer is discharged through use of centrifugal force generated by rotation, IPA (isopropyl alcohol) drying in which the pure water on the wafer is replaced with IPA and the IPA is vaporized to dry the wafer, and some other drying. However, there has been a problem with these general drying treatments in that fine patterns formed on the wafer come into contact with one another when drying due to surface tension of the liquid remaining on the wafer, resulting in a blockage.
In order to solve such a problem, there has been proposed supercritical drying in which surface tension is zero. In the supercritical drying, after the wafer cleaning treatment, the liquid on the wafer is replaced with another solvent such as IPA, which is finally replaced with a supercritical drying solvent; and the wafer is introduced into a supercritical chamber while the surface thereof is held wet with the IPA. Subsequently, carbon dioxide brought into a supercritical state (supercritical CO2 fluid) is supplied to the chamber. The IPA on the wafer is gradually dissolved into the supercritical CO2 fluid, and discharged from the chamber along with the supercritical CO2 fluid. Thereby, the IPA on the wafer is replaced with the supercritical CO2 fluid. Subsequently, a pressure inside the chamber is decreased and the supercritical CO2 fluid is subjected to a phase change to gaseous CO2, to complete drying of the wafer.
However, with a critical pressure of carbon dioxide being about 7.5 MPa, there has been a problem in that a thick metal-made chamber having performance resistant to a pressure not smaller than the above the critical pressure is required as a treatment facility, and therefore, the cost of the chamber as a single body is increased. Thus, cost of the device as a total is increased.
There is also known a method for performing drying not by using the supercritical CO2 fluid as the drying solvent, but by bringing the IPA, which is a replacement solution for rinsing pure water after chemical-solution cleaning, itself into a supercritical state and evaporating and discharging the IPA. With the supercritical pressure of the IPA being about 5.4 MPa, a thickness required for the chamber is smaller than that in the case of using the supercritical CO2 fluid, thereby allowing reduction in cost of the device. Further, since the IPA, which serves as the solution to be replaced with pure water, is directly brought into the supercritical state, a step of replacing the IPA with the supercritical CO2 fluid as performed in a carbon supercritical is unnecessary. Moreover, a CO2 supply system, a boosting device, and the like are unnecessary, thus allowing cost reduction.
However, there has been a problem with the drying method of bringing an organic solvent, such as IPA, into the supercritical state as thus described in that a metal material film and a polysilicon film formed on a semiconductor substrate are etched, thereby causing deterioration in electric characteristics of a semiconductor device.